Src-NADH dehydrogenase subunit 2 complex and recognition memory of imprinting in domestic chicks.

Src is a non-receptor tyrosine kinase participating in a range of neuronal processes, including synaptic plasticity. We have recently shown that the amounts of total Src and its two phosphorylated forms, at tyrosine-416 (activated) and tyrosine-527 (inhibited), undergoes time-dependent, region-specific learning-related changes in the domestic chick forebrain after visual imprinting. These changes occur in the intermediate medial mesopallium (IMM), a site of memory formation for visual imprinting, but not the posterior pole of the nidopallium (PPN), a control brain region not involved in imprinting. Src interacts with mitochondrial genome-coded NADH dehydrogenase subunit 2 (NADH2), a component of mitochondrial respiratory complex I. This interaction occurs at brain excitatory synapses bearing NMDA glutamate receptors. The involvement of Src-NADH2 complexes in learning and memory is not yet explored. We show for the first time that, independently of changes in total Src or total NADH2, NADH2 bound to Src immunoprecipitated from the P2 plasma membrane-mitochondrial fraction: (i) is increased in a learning-related manner in the left IMM 1 h after the end of training; (ii), is decreased in the right IMM in a learning-related way 24 h after training. These changes occurred in the IMM but not the PPN. They are attributable to learning occurring during training rather than a predisposition to learn. Learning-related changes in Src-bound NADH2 are thus time- and region-dependent.

Filial imprinting in domestic chicks; cytoplasmic polyadenylation element binding protein 3, predispositions and learning.

Visual imprinting is a learning process, whereby young animals come to prefer a visual stimulus after exposure to it (training). Available evidence indicates that the intermediate medial mesopallium (IMM) in the domestic chick forebrain is a site of memory formation during visual imprinting. We have found previously that cytoplasmic polyadenylation element binding protein 3 in the P2 plasma membrane-mitochondrial fraction (CPEB3-P2) is upregulated in a learning-dependent way in the left IMM 24 h after training. CPEB3 has two forms, soluble and aggregated. Soluble CPEB3 represses translation; the aggregated form (CPEB3-AF) is amyloid-like and can promote translation. Our previous study did not show which of these two forms is increased after imprinting. We have now resolved this matter by measuring, 24 h after training, CPEB3-P2 and CPEB3-AF in the IMM and a control brain region, the posterior pole of nidopallium (PPN). The methods include imprinting training with a visual stimulus, behavioral measurement of preference, preparation of aggregated CPEB3, western immunoblotting, quantitation of proteins, statistical linear modeling. Only in the left IMM were the level of CPEB3-AF and learning strength correlated, increased CPEB3-AF level reflecting a predisposition to learn readily. CPEB3-P2 level also increased with learning strength in the left IMM, but as a result of learning. No correlations were detected in the right IMM or PPN. We propose two separate systems, both modulating synaptic strength through control of local translation. They are represented by CPEB3-AF (associated with a predisposition to learn) and soluble CPEB3 (associated with learning itself).

Src and Memory: A Study of Filial Imprinting and Predispositions in the Domestic Chick.

Visual imprinting is a learning process whereby young animals come to prefer a visual stimulus after exposure to it (training). The available evidence indicates that the intermediate medial mesopallium (IMM) in the domestic chick forebrain is a site of memory formation during visual imprinting. We have studied the role of Src, an important non-receptor tyrosine kinase, in memory formation. Amounts of total Src (Total-Src) and its two phosphorylated forms, tyrosine-416 (activated, 416P-Src) and tyrosine-527 (inhibited, 527P-Src), were measured 1 and 24 h after training in the IMM and in a control brain region, the posterior pole of nidopallium (PPN). One hour after training, in the left IMM, we observed a positive correlation between the amount of 527P-Src and learning strength that was attributable to learning, and there was also a positive correlation between 416P-Src and learning strength that was attributable to a predisposition to learn readily. Twenty-four hours after training, the amount of Total-Src increased with learning strength in both the left and right IMM, and amount of 527P-Src increased with learning strength only in the left IMM; both correlations were attributable to learning. A further, negative, correlation between learning strength and 416P-Src/Total-Src in the left IMM reflected a predisposition to learn. No learning-related changes were found in the PPN control region. We suggest that there are two pools of Src; one of them in an active state and reflecting a predisposition to learn, and the second one in an inhibited condition, which increases as a result of learning. These two pools may represent two or more signaling pathways, namely, one pathway downstream of Src activated by tyrosine-416 phosphorylation and another upstream of Src, keeping the enzyme in an inactivated state via phosphorylation of tyrosine-527.

Chicken cognin interactome and the memory of filial imprinting.

Visual imprinting is a learning process whereby young animals come to prefer a visual stimulus after exposure to it (training). The intermediate medial mesopallium in the domestic chick forebrain is critical for visual imprinting and contributes to molecular regulation of memory formation. Criteria used to infer that a change following training is learning-related have been formulated and published. Cognin (protein disulphide isomerase) is one of several identified plasma membrane and mitochondrial proteins that are upregulated in a learning-related way 24 hours after training. Since virtually nothing is known about the cognin interactome, we have used immunoaffinity chromatography and mass spectrometry to identify proteins that interact with cognin in the cytoplasmic and plasma membrane-mitochondrial fractions. As the learning-related upregulation of cognin has been shown to occur in the plasma membrane-mitochondrial fraction and not in the cytoplasmic fraction, we studied the effect of training on three cognin-interacting partners in the plasma membrane-mitochondrial fraction: the b5 subunit of mitochondrial ATP synthase and the alpha-2 and alpha-3 subunits of sodium-potassium ATPase. Learning-related upregulation was found in the left intermediate medial mesopallium 24 hours after training for the b5 subunit of mitochondrial ATP synthase and the alpha-2 subunit of sodium-potassium ATPase. The hemispheric asymmetry revealed here is consistent with the predominance of many other learning-related effects in the left intermediate medial mesopallium. The alpha-2 subunit of sodium-potassium ATPase is mainly expressed in astrocytes, supporting a role for these glial cells in memory.